Apparatus and methods for analyzing images, and in particular for image processing and analysis, which are useful in inspection of patterned objects, are well known in the art.
The following references describe image processing methods which may be useful in understanding the present invention:    C. Gonzalez and P. Wintz, Digital Image Processing, Addison Wesley, Reading, Mass., 1987; and    John C. Russ, The Image Processing Handbook, CRC Press, 1994.
The following references describe edge detection methods which may be useful in understanding the present invention:    D. Marr and E. Hildreth, Theory of Edge Detection, Proceedings of the Royal Society of London; and    M. Chapron, “A new chromatic edge-detector used for color image segmentation”, 11th APR International Conference on Pattern Recognition.
The following references describe color image segmentation methods which may be useful in understanding the present invention:    Philippe Pujas and Marie-Jose Aldon, “Robust Colour Image Segmentation”, 7th International Conference on Advanced Robotics, San Filiu de Guixols, Spain, Sep. 22, 1995, and    Leila Shararenko, Maria Petrou, and Josef Kittler, “Automatic Watershed Segmentation of Randomly Textured Colour Images, IEEE.
U.S. Pat. No. 4,758,888 to Lapidot describes a method of and means for inspecting workpieces traveling along a production line, including on-line inspection for flaws without interrupting the progress or workpieces along the production line.
U.S. Pat. No. 5,586,058 and U.S. Pat. No. 5,619,429 to Aloni et al. describe apparatus and methods for inspecting patterned objects and detecting defects therein, including inspecting a binary level representation of the object, inspecting a gray level representation of the object, and preferably reinspecting the grayscale representation of the object to filter false alarms and to classify defects.
U.S. Pat. No. 5,774,572 to Caspi describes an automatic visual inspection system, which is operative to convolve a 2-dimensional digital gray scale image of an object with a filter function related to the second derivative of a Gaussian function forming a 2-dimensional convoluted image have signed values. The location of an edge in the object is achieved by finding zero crossings between adjacent oppositely signed values.
U.S. Pat. No. 5,774,573 to Caspi et al. describes a visual inspection system which uses convolution of a 2-dimensional digital gray scale image of an object with a filter function related to the second derivative of a Gaussian function forming a 2-dimensional convolved imaged having signed values. The convolution of Caspi et al. can be performed with a difference-of-two-Gaussians, one positive and one negative.
PCT Application IL98/00393 describes inspection of printed circuit boards using color, including the use of color to identify certain types of conditions, such as conductor oxidation, using color.
PCT Application IL98/00477 describes methods for analytically representing an image so that morphological operations such as dilation, erosion, and scale measurement may be performed on non-binary pixels, preferably more efficiently than using previous methods.
Applicant's unpublished Israel Patent Application No. 125929 describes article inspection systems and methods, including an improved image acquisition system. Methods which may be useful in image analysis are described in the following publication:    Dorin Comaniciu and Peter Meer, “Distribution Free Decomposition of Multivariate Date”, SPR '98 Invited Submission, Department of Electrical and Computer Engineering, Rutgers University, Piscataway, N.J. 08855, USA.
The disclosures of all publications mentioned above and throughout the specification and of the publications cited therein are hereby incorporated by reference.